The cranking and start up of engines fueled by hydrocarbon-based fuels, such as gasoline, can exhibit the undesirable effect of discharging deleterious exhaust emissions or gases into the atmosphere. These exhaust gas emissions, prior to any pre-discharged treatment, usually contain environmentally unacceptable components as NO.sub.x, CO, and unburned hydrocarbons.
It can be appreciated when one considers the number of automobiles in daily service, that the amount of untreated engine exhaust which is delivered into the atmosphere is virtually immeasurable. In spite of the number of catalytic converters presently in service which treat the exhaust gas prior to its discharge, the volume which flows past cold catalyst beds and consequently remains marginally treated, is still considerable.
In brief, the issue of a clean atmospheric environment suggests future air quality problems on a worldwide basis. Nonetheless, each step even though minor, toward limiting the daily rate of pollutant gases which enter the atmosphere, must be welcome.
One common practice known and accepted commercially for treating exhaust gases prior to their release into the atmosphere, is to convert the gases into less noxious fumes. A widely used and successfully practiced treatment for hot exhaust gas which leaves an automobile or truck engine at a temperature of up to 2000.degree. F., is to bring the gas into contact with an active catalyst to prompt the desired chemical conversion. This method is designed to receive and treat a steady flow of hot exhaust gas as it is being produced from an internal combustion engine.
Physically, even a brief contact period between a heated catalyst material which should preferably be at least 700.degree.-900.degree. F. and a stream of the engine exhaust gas, can be effective in achieving conversion of the gas into a less harmful condition. It is important to note however that this reaction, if utilized to its maximum potential, requires a preferred operating catalyst temperature in excess of about 900.degree. F.
It is known, for example, that for initial start up of any engine equipped vehicle having an exhaust system catalytic converter, the catalyst will in all probability not be at a sufficiently high temperature to be effective. Thus, for the first several minutes or miles of the engine's operation, exhaust emissions will enter the atmosphere only marginally treated.
During a cold engine's start up, the engine's exhaust gas becomes progressively hotter as engine parts become heated. As the initially produced gas contacts the catalyst, the latter will likewise become heated from ambient to the temperature of the exhaust gas.
During this initial or warm-up period as noted, there will be minimal, if any reaction in exhaust gas conversion to a less noxious state since the temperature of the catalyst is too low to promote such a reaction. Subsequent to the warm-up period, however, due to heat exchange with the hot exhaust gas stream with the catalytic bed, the latter will be heated to a temperature at which it is capable of achieving maximum effectiveness.
It is known to initially heat the catalyst heater element using the vehicle's ignition system battery. By initially applying the full power of the ignition battery to the catalyst heating element, the catalyst will after a period, become sufficiently hot to prompt exhaust gas conversion.
In any such heating operation however, the characteristics of an electrical resistance heater are such that unless the battery has its rated capability and is fully charged, it will be drained by the catalyst preheating step. Unfortunately, after the catalyst is heated to a desired operating temperature, the battery may lack the necessary power particularly under cold conditions to crank and start the engine.
The maximum energy obtainable from a storage battery when it is at a particular state of charge and temperature will vary with the rate at which the energy is withdrawn. In other words, to realize maximum efficiency of energy transfer from a battery to an external load such as an exhaust gas heated catalyst heater, a specific current draw program must be followed. This would assure a maximum level of energy remaining in the battery to power the crank and engine start cycle.
In brief, injudicious use of the ignition battery, in view of the battery's limited capacity, can result in a fully heated catalyst, yet a condition which prohibits engine start up.
In addition, rapid catalyst heating which tends to drain a battery and which requires rapid recharging, can have an adverse effect on the battery's life. This sort of rapid discharge schedule and subsequent recharging is a sure invitation to accelerate battery replacement.